1. Field of the Invention
The present invention relates to a method preparing block copolyether-ester-amides. In the first step, polyether polyol is reacted with caprolactam or other lactam in the presence of a catalyst to form an amino group-terminated prepolymer. The prepolymer is then reacted with a dicarboxylic acid to produce high molecular weight block copolymers.
2. Description of the Related Art
Methods of synthesizing block copolyether-ester-amides have been disclosed in various patents. French Pat. Nos. 1,444,437 and 2,178,205 disclose methods which comprise reacting a dicarboxyl-end polyamide with a polyoxyalkylene glycol to produce block copolymers used as anti-static agents. The molecular weight of block copolymers prepared by these methods, however, is rather low.
U.S. Pat. No. 4,332,920 (ATO Chimie, France) discloses a method which comprises reacting a dicarboxyl-end polyamide with a poly(tetramethylene ether) glycol (PTMEG) in the presence of a tetraalkylorthotitanate catalyst. The carboxy-end polyamide used in this method can be a polyamide with a carboxylic acid end group obtained from lactams or amino acids having 4-14 carbon atoms, or a condensation product of a dicarboxylic acid and a diamine, such as low molecular weight nylon-6,6, nylon-6,9, nylon-6,12, or nylon-9,6. The products exhibit good mechanical properties and can be processed by conventional machinery.
Japan Pat. No. 57-24808 discloses a single-step synthesis method. An amino acid having more than 10 carbon atoms, PTMEG, and dicarboxylic acid are copolycondensed in the presence of water to form block copolyether-ester-amides. Japan Pat. No. 58-21095 discloses a similar method in which aminocapric acid is used instead of higher amino acids.
The method disclosed in Japan Pat. 57-24808 involves reaction of an amino acid having more than 10 carbon atoms, PTMEG, and dicarboxylic acid in the presence of water. During the reaction process, carboxylic acid groups are first reacted with an amino group rather than the hydroxy group of PTMEG, due to the higher reactivity of the amino group. Thus, oligomeric polyamides with carboxyl end groups are first formed, and then condensed with PTMEG to form block copolyether-ester-amides. In fact, in the above methods, either one step or two step, a carboxy-end polyamide exists.
When a carboxy-end polyamide derived from caprolactam is used instead of one derived from higher lactams, the miscibility becomes a severe problem. The carboxy-end polyamide derived from caprolactam is immiscible with PTMEG. During the reaction, however, phase separation occurs, and the caprolactam-based block copolyether-ester-amide possesses low molecular weight, is opaque, and exhibits poor mechanical properties.
Japan Pat. No. 61-278530 discloses a method wherein the problem of immiscibility of carboxy-end polycaprolactam and PTMEG is solved by using a compatibilizer. In this method, carboxy-end polycaprolactam is reacted with PTMEG in the presence of at least 70 wt% of caprolactam (base on polyamide segment) which is used as a compatibilizer. The presence of caprolactam renders the reaction mixture homogeneous, and a transparent product is obtained. The use of such a high percentage of caprolactam, however, reduces the conversion.
West German Pat. No. 213,577 discloses another method for preparing nylon-6 based block copolyether-ester-amides. In this method, polyether polyol is first reacted with dicarboxylic acid, and the polyether with carboxyl end group is then reacted with caprolactam. The resultant product, however, is very brittle.
Clearly, the miscibility of carboxy-end polyamide and polyether polyol poses a substantial problem in preparing the block copolyether-ester-amides by the above method. When the reaction mixture is homogeneous, as is the case when carboxy-end polyamide is derived from higher carbon atom raw material such as nylon-11 and nylon-12, or a compatibilizer is present, a good result is observed. Otherwise, the result is a low molecular weight block copolyether-ester-amide with less than desirable properties. The immiscibility problem is particularly severe between carboxy-end polycaprolactam and PTMEG.